Fabrication of a vertical fin field effect transistor with reduced dimensional variations

ABSTRACT

A method of forming a fin field effect transistor (finFET) having fin(s) with reduced dimensional variations, including forming a dummy fin trench within a perimeter of a fin pattern region on a substrate, forming a dummy fin fill in the dummy fin trench, forming a plurality of vertical fins within the perimeter of the fin pattern region, including border fins at the perimeter of the fin pattern region and interior fins located within the perimeter and inside the bounds of the border fins, wherein the border fins are formed from the dummy fin fill, and removing the border fins, wherein the border fins are dummy fins and the interior fins are active vertical fins.

BACKGROUND Technical Field

The present invention generally relates to compensation for fin profilevariations, and more particularly to an approach for reducing thedimensional variations between edge fins and interior fins whilemaintaining device density by removing edge fins.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and finFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the finFET can be an upright slab of thin rectangular Si,commonly referred to as the fin with a gate on the fin, as compared to aMOSFET with a single gate in the plane of the substrate. Depending onthe doping of the source and drain, an n-FET or a p-FET may be formed.

Examples of FETs can include a metal-oxide-semiconductor field effecttransistor (MOSFET) and an insulated-gate field-effect transistor(IGFET). Two FETs also may be coupled to form a complementary metaloxide semiconductor (CMOS), where a p-channel MOSFET and n-channelMOSFET are coupled together.

With ever decreasing device dimensions, forming the individualcomponents and electrical contacts become more difficult. An approach istherefore needed that retains the positive aspects of traditional FETstructures, while overcoming the scaling issues created by formingsmaller device components.

SUMMARY

In accordance with an embodiment of the present principles, a method isprovided for forming a fin field effect transistor (finFET) havingfin(s) with reduced dimensional variations. The method includes thesteps of forming a dummy fin trench within a perimeter of a fin patternregion on a substrate, and forming a dummy fin fill in the dummy fintrench. The method further includes the step of forming a plurality ofvertical fins within the perimeter of the fin pattern region, includingborder fins at the perimeter of the fin pattern region and interior finslocated within the perimeter and inside the bounds of the border fins,wherein the border fins are formed from the dummy fin fill. The methodfurther includes the step of removing the border fins, wherein theborder fins are dummy fins and the interior fins are active verticalfins.

In accordance with an embodiment of the present principles, a method isprovided for forming a fin field effect transistor (finFET) havingfin(s) with reduced dimensional variations. The method includes thesteps of forming at least one dummy fin trench in a substrate, andforming a dummy fin fill in the at least one dummy fin trench. Themethod further includes the step of forming one or more dummy fins fromthe dummy fin fill and one or more vertical fins from the substrate by asidewall image transfer process. The method further includes the step ofremoving the one or more dummy fins by a selective etch, while leavingthe one or more vertical fins on the substrate. The method furtherincludes the steps of forming a dielectric layer on the one or morevertical fins and at least a portion of the substrate, wherein thedielectric layer fills in at least a portion of the at least one dummyfin trench, and forming a gate structure on the one or more verticalfins.

In accordance with another embodiment of the present principles, a finfield effect transistor (finFET) having fin(s) with reduced dimensionalvariations is provided. The device includes a plurality of vertical finswithin a perimeter of a fin pattern region on a substrate. The devicefurther includes a step formed in the substrate around the plurality ofvertical fins, and a dielectric layer on the step and at least a portionof the plurality of vertical fins.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a top view of an array of vertical fins on a region of asubstrate, in accordance with an exemplary embodiment;

FIG. 2 is a top view of a layout of fin pattern regions on a substrate,in accordance with an exemplary embodiment;

FIG. 3 is a cross-sectional side view of a substrate with a hardmasklayer, in accordance with an exemplary embodiment;

FIG. 4 is a cross-sectional side view of a substrate with a hardmasklayer after formation of dummy fin trenches, in accordance with anexemplary embodiment;

FIG. 5 is a cross-sectional side view of a dummy fin fill in the dummyfin trenches, in accordance with an exemplary embodiment;

FIG. 6 is a cross-sectional side view of the substrate and dummy finfill with a flat uniform surface after removal of the hardmask, inaccordance with an exemplary embodiment;

FIG. 7 is a cross-sectional side view of a masking layer, a mandrellayer, and a fin template layer on the substrate and dummy fin fill, inaccordance with an exemplary embodiment;

FIG. 8 is a cross-sectional side view of a plurality of photo maskblocks on the mandrel templates and sacrificial mandrels, in accordancewith an exemplary embodiment;

FIG. 9 is a cross-sectional side view of a plurality of spacers on thesacrificial mandrels and fin template layer, in accordance with anexemplary embodiment;

FIG. 10 is a cross-sectional side view of a plurality of spacers on thefin template layer on the substrate, in accordance with an exemplaryembodiment;

FIG. 11 is a cross-sectional side view of a plurality of spacers on thefin templates and vertical fins, in accordance with an exemplaryembodiment;

FIG. 12 is a cross-sectional side view of a plurality of vertical finsand dummy fins in a fin pattern region after removal of the spacers andfin templates, in accordance with an exemplary embodiment;

FIG. 13 is a cross-sectional side view of a plurality of vertical finsin a fin pattern region after removal of the dummy fins and fin fill, inaccordance with an exemplary embodiment;

FIG. 14 is a cross-sectional side view of a bottom spacer layer andisolation region formed on a portion of the substrate, in accordancewith an exemplary embodiment;

FIG. 15 is a cross-sectional side view of a gate dielectric layer formedon the exposed portions of the vertical fins, in accordance with anexemplary embodiment;

FIG. 16 is a cross-sectional side view of a work function layer and agate electrode formed on the gate dielectric layer, in accordance withan exemplary embodiment;

FIG. 17 is a top view of a gate structure on a plurality of verticalfins with source/drains at opposite ends of the fins, in accordance withan exemplary embodiment;

FIG. 18 is a top view of a gate structure on a plurality of verticalfins with source/drains at opposite ends of the fins, in accordance withan exemplary embodiment;

FIG. 19 is a cross-sectional side view of a top spacer formed on areduced height gate dielectric layer, work function layer, and gateelectrode layer, in accordance with an exemplary embodiment; and

FIG. 20 is a cross-sectional side view of an interlayer dielectric andtop source/drains formed on the top spacer and top portions of thevertical fins, in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

Principles and embodiments of the present disclosure relate generally tocontrolling variations in vertical fin dimensions of fins located alongthe perimeter of a fin pattern region by forming dummy fins along theperimeter of the fin pattern region. After forming both functional anddummy fins in a vertical fin pattern, the dummy fins may be removed toleave remaining vertical fins with more consistent dimensions. The dummyfins may be made of a more easily removed and/or cheaper material thatmay be selectively etched relative to the functional vertical fins.

Due to micro-loading effects (i.e., decreased local etchantconcentrations), fins at a fin array edge usually end up with differentprofiles (e.g., more sloped and wider) than interior fins inside theborder fins. In various embodiments, the vertical fins remaining afterremoval of the dummy fins may have a more uniform profile. Differencesin the pattern density may affect the etch rate of a semiconductormaterial being used to form a vertical fin. This may be particularlypronounced along a perimeter of a fin pattern region, where the fins atthe border of the region may have a neighboring fin on only one side.Adjustment of the vertical fin pattern to include a dummy fin adjacentto an intended border fin, where the dummy fin may be removed later inthe process, may compensate for the difference in fin pattern density atthe perimeter.

Principles and embodiments of the present disclosure also relategenerally to selectively forming and removing dummy fins along theperimeter of and/or within a fin pattern region as a fin-cut process tofabricate a predetermined pattern of active fin(s) within a fin patternregion. After forming both functional and dummy fins in a vertical finpattern, the dummy fins may be removed to leave remaining vertical finsin a predetermined arrangement on the substrate. The placement of one ormore dummy fins may also define the location of a subsequently formedisolation region within a pattern of active fin(s).

Exemplary applications/uses to which the present principles can beapplied include, but are not limited to: formation of vertical finFETs,complementary metal oxide silicon (CMOS) field effect transistors (FETs)formed by coupled finFETs, and digital gate devices (e.g., NAND, NOR,XOR, etc.).

In various embodiments, the materials and layers may be deposited byphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), molecular beam epitaxy (MBE), or any of thevarious modifications thereof, for example plasma-enhanced chemicalvapor deposition (PECVD), metal-organic chemical vapor deposition(MOCVD), low pressure chemical vapor deposition (LPCVD), electron-beamphysical vapor deposition (EB-PVD), and plasma-enhanced atomic layerdeposition (PE-ALD). The depositions may be epitaxial processes, and thedeposited material may be crystalline. In various embodiments, formationof a layer may be by one or more deposition processes, where, forexample, a conformal layer may be formed by a first process (e.g., ALD,PE-ALD, etc.) and a fill may be formed by a second process (e.g., CVD,electrodeposition, PVD, etc.).

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It should be noted that certain features may not be shown in all figuresfor the sake of clarity. This is not intended to be interpreted as alimitation of any particular embodiment, or illustration, or scope ofthe claims.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, which is a top view of anarray of vertical fins on a region of a substrate, in accordance with anexemplary embodiment.

In one or more embodiments, a plurality of vertical fins may be arrangedin a pattern on a substrate, where the vertical fins forming a finpattern 20 (e.g., a M×N array) may include border fins 50 at theperimeter of the fin pattern region 10 and interior fins 90 locatedwithin the perimeter and inside the bounds of the border fins 50. A finpattern region 10 may be defined by a difference in the fin arrangementcompared to one or more neighboring fin pattern regions on the substrate100 that distinguish the fin pattern regions, where the difference maybe, for example, different fin sizes (i.e., fin dimensions) fin pitches,array dimensions (e.g., M×N vs. X×Y, M≠X and N≠Y). A fin pattern region10 may also be defined by an isolation region between one or moreneighboring fin pattern regions, and/or fin-cut regions, where there hasbeen an increase in the distance between adjacent fins, for example byremoval of vertical fin(s).

In various embodiments, the border fins 50 may include the fin(s) in thesame column along opposite edges of a fin pattern region 10. Fin(s) inthe same row at the top and/or bottom of the same fin pattern region mayalso be border fin(s) 50, whereas fin(s) inside this perimeter of borderfins would be interior fins 90.

A border fin 50 may have a different profile (e.g., different taperangle) and/or dimensions (e.g., wider) than adjacent interior fin(s) 90due to local variations in the etching process (e.g., decreased etchingrate) used to form the vertical fins in a fin pattern region 10 on asubstrate 110. Without intending to be bound by theory, it is believedthat the concentration of reactive species depends on the fin patterndensity within a certain radius, and that the etchant concentrationincreases with decreasing fin pattern density. The fin density alongedges and at corners may be less because the border fins 50 only haveadjacent fins on one side, and fins at the corners are exposed on twosides.

Principles and embodiments of the present disclosure relate to adjustinga fabrication process to address the different local densitiesexperienced by the vertical fins in a fin pattern region 10 by formingsacrificial fins in place of the border fins 50 at the perimeter of thefin pattern region 10. By adjusting the fin pattern 20 to include atleast one additional column of sacrificial vertical fin(s) along each ofthe edges of the fin pattern region 10, the variation in vertical finsize and/or profile may be compensated for. Device variations due to thevariation in vertical fin size and/or profile may be avoided byselectively forming the border fins 50 of a material that may bepreferentially etched relative to the interior fins 90, and selectivelyremoving the border fins 50, as sacrificial dummy fins, to leave theinterior fins 90 for device (e.g., finFET) fabrication. The interiorfins 90 may have more consistent profiles and/or dimensions leading toreduced device performance variation, where the interior fins may beretained as active vertical fins for the fabrication of vertical orhorizontal finFET(s).

FIG. 2 is a top view of a layout of fin pattern regions 10 on asubstrate, in accordance with an exemplary embodiment.

In one or more embodiments, a plurality of fin pattern regions 10 withdiffering fin patterns 20 may be laid out on a substrate 110, where thedifferent fin patterns may be predetermined to fabricate integratedcircuit devices for different components, for example, dynamic randomaccess memory (DRAM), static random access memory (SRAM), registers,processing cores, graphics processors, memory, heat and/or processingcontrol circuits, input-output controllers, etc. Pattern region gap(s)12 may be predetermined spaces present between different fin patternregions 10, where the pattern region gaps may include spaces formed bythe removal of the border fins 50 in neighboring fin pattern regions 10.Pattern region gaps 12 may be isolation regions to electrically separatedifferent components and/or devices.

In various embodiments, more than one column and/or row of fins at theperimeter of a fin pattern region 10 may be formed as dummy fin(s) andremoved, where the width of a pattern region gap 12 may be determined bythe number of columns and/or rows of dummy fin(s) formed and removed.

FIG. 3 is a cross-sectional side view of a substrate with a hardmasklayer, in accordance with an exemplary embodiment.

In one or more embodiments, a substrate 110 may be a semiconductor or aninsulator with an active surface semiconductor layer. The substrate maybe crystalline, semi-crystalline, microcrystalline, or amorphous. Thesubstrate may be essentially (i.e., except for contaminants) a singleelement (e.g., silicon), primarily (i.e., with doping) of a singleelement, for example, silicon (Si) or germanium (Ge), or the substratemay include a compound, for example, Al₂O₃, SiO₂, GaAs, SiC, or SiGe.The substrate may also have multiple material layers, for example, asemiconductor-on-insulator substrate (SeOI), a silicon-on-insulatorsubstrate (SOI), germanium-on-insulator substrate (GeOI), orsilicon-germanium-on-insulator substrate (SGOI). The substrate may alsohave other layers forming the substrate, including high-k oxides and/ornitrides. In one or more embodiments, the substrate 110 may be a siliconwafer. In various embodiments, the substrate may be a single crystalsilicon (Si), silicon germanium (SiGe), or III-V semiconductor (e.g.,GaAs) wafer, or have a single crystal silicon (Si), silicon germanium(SiGe), or III-V semiconductor (e.g., GaAs) surface/active layer.

In one or more embodiments, a hardmask layer 120 may be formed on anexposed surface of the substrate 110. The hardmask layer 120 may beformed by a thermal process, such as, for example, oxidation ornitridation of the top semiconductor layer, or the hardmask layer may bedeposited, for example, by CVD or PVD. A combination of the variousprocesses may also be used to form hardmask layer 120.

In various embodiments, the hardmask layer may be an oxide, for example,silicon oxide (SiO), a nitride, for example, a silicon nitride (SiN), oran oxynitride, for example, silicon oxynitride (SiON), or combinationsthereof. In various embodiments, the hardmask layer 120 may be siliconnitride (SiN), for example, Si₃N₄. The hardmask layer 120 may be asingle layer for example, a silicon nitride (SiN) layer, or the hardmasklayer may include two or more layers, for example a silicon oxide (SiO)liner layer between the substrate surface and a silicon nitride (Si₃N₄)top layer. The liner layer may be a material different from a top layer130, where the liner layer may act as an etch stop layer.

In one or more embodiments, the hardmask layer 120 may have a thicknessin the range of about 20 nm to about 100 nm, or in the range of about 35nm to about 75 nm, or in the range of about 45 nm to about 55 nm,although other thicknesses are contemplated. A liner layer may have athickness in the range of about 1 nm to about 10 nm, or in the range ofabout 2 nm to about 5 nm.

FIG. 4 is a cross-sectional side view of a substrate with a hardmasklayer after formation of dummy fin trenches, in accordance with anexemplary embodiment.

In one or more embodiments, a photoresist layer 130 may be formed on thehardmask layer 120. The photoresist layer 130 may be a temporary resist(e.g., poly methyl methacrylate (PMMA)) that may be deposited on thehardmask layer 120, patterned, and developed to expose portions of thehardmask layer 120. The photoresist layer may be a positive resist or anegative resist.

In one or more embodiments, at least a portion of the hardmask layer 120may be masked by a photoresist layer 130 that can be patterned anddeveloped to expose portions of the hardmask layer 120. Exposed portionsof the hardmask layer 120 and underlying substrate 110 may be removed toform one or more dummy fin trenches 140, where the dummy fin trenchesmay be formed by a directional, dry plasma etch (e.g., reactive ion etch(RIE)).

In one or more embodiments, one or more sections of the substrate 110may be removed to form the dummy fin trenches 140, where the substrate110 may be removed to a depth approximately equal to or greater than anintended height of one or more vertical fin(s) to be formed from thesubstrate material adjacent to the dummy fin trench. In variousembodiments, the depth of the dummy fin trench(es) may be in the rangeof 20 nm to about 200 nm, or about 40 nm to about 150 nm, or about 50 nmto about 100 nm, where the depth is measured from the top of thesubstrate 110 to the bottom surface of the trench. Other depths are alsocontemplated.

In various embodiments, formation of the dummy fin trench 140 may form astep with a ledge around one or more interior fins 90, where the dummyfin trench may subsequently form an isolation region having a depthgreater than a depth of a bottom source/drain.

In various embodiments, the width of the one or more dummy fin trenches140 may be in the range of about 30 nm to about 300 nm, or in the rangeof about 50 nm to about 200 nm, or in the range of about 80 nm to about150 nm. In various embodiments, the width of the dummy fin trench 140may be sufficient to form one dummy fin at the perimeter of a finpattern region 10, where the dummy fin is located the same pitchdistance from an adjacent interior fin 90, as the pitch between adjacentinterior fins 90 in the same fin pattern 20.

FIG. 5 is a cross-sectional side view of a dummy fin fill in the dummyfin trenches, in accordance with an exemplary embodiment.

In one or more embodiments, a dummy fin fill 150 may be formed in theone or more dummy fin trenches 130, where the dummy fin fill may be ablanket deposition that fills the dummy fin trenches 140. The dummy finfill may extend above the hardmask layer 120.

In one or more embodiments, the dummy fin fill 150 may be a materialwith an etch rate for an intended directional anisotropic etch (e.g.,RIE) that is comparable to the etch rate of the substrate material, forexample, a dummy fin fill 150 may be amorphous silicon (a-Si),poly-crystalline silicon (p-Si), amorphous silicon-germanium (a-SiGe),or poly-crystalline silicon-germanium (p-SiGe) when the substrate issingle crystal silicon (Si).

In various embodiments, dummy fin fill 150 may be an amorphous orpoly-crystalline III-V semiconductor material when the substrate is asingle crystal III-V semiconductor material, where the amorphous orpoly-crystalline III-V semiconductor material has a comparable etch rateto the single crystal III-V semiconductor material.

FIG. 6 is a cross-sectional side view of the substrate and dummy finfill with a flat uniform surface after removal of the hardmask, inaccordance with an exemplary embodiment.

In one or more embodiments, a portion of the dummy fin fill 150 and theremaining portion of the hardmask 120 may be removed to expose a surfaceof the substrate 110 and dummy fin fill 150, where the surface of thesubstrate and dummy fin fill may be flat, smooth, and uniform. Invarious embodiments, the portion of the dummy fin fill 150 and hardmasklayer 120 may be removed by a chemical-mechanical polishing (CMP). Invarious embodiments, the remaining portion of the hardmask 120 and/ordummy fin fill 150 may be removed by etching, and the surface preparedby CMP to provide a smooth, flat surface.

FIG. 7 is a cross-sectional side view of a masking layer, a mandrellayer, and a fin template layer on the substrate and dummy fin fill, inaccordance with an exemplary embodiment.

In one or more embodiments, a fin template layer 160 may be formed on atleast a portion of the surface of the dummy fin fill 150 and substrate110. A mandrel layer 170 may be formed on at least a portion of the fintemplate layer 160, where the mandrel layer may be utilized to formsacrificial mandrels for a sidewall image transfer (SIT) process offorming vertical fin(s). A masking layer 180 may be formed on at least aportion of the mandrel layer 170, where the masking layer may be a hardmask for etching portions of the mandrel layer 170. A photo mask layermay be formed and patterned on the masking layer 180, where the photomask layer may be a soft mask.

In one or more embodiments, the photo mask layer may be patterned anddeveloped to form photo mask blocks 191, and expose underlying portionsof the masking layer 180. The photo mask blocks 191 may protect thecovered portion of the masking layer 180, while exposed portions of themasking layer 180 may be etched to form mandrel templates 181 on themandrel layer 170. In one or more embodiments, photo mask blocks 191 maybe a soft mask, for example, PMMA. One or more photo mask blocks 191 maydefine the width, length, and pitch of the one or more mandrel templatesand thereby, a pitch of the vertical fins.

In various embodiments, the pitch, P₁, between adjacent photo maskblocks 191 and/or mandrel template(s) 181 may be in the range of about20 nm to about 200 nm, or in the range of about 30 nm to about 100 nm,or in the range of about 30 nm to about 50 nm, or about 42 nm.

FIG. 8 is a cross-sectional side view of a plurality of photo maskblocks on the mandrel templates and sacrificial mandrels, in accordancewith an exemplary embodiment.

In one or more embodiments, the masking layer 180 may be etched to formone or more mandrel template(s) 181, where the photo mask blocks 191defined the width, length, and location of the mandrel template(s) 181on the substrate mandrel layer 170.

In one or more embodiments, a portion of the mandrel layer 170 may beremoved to form one or more sacrificial mandrels 171 on the fin templatelayer 160.

In various embodiments, the mandrel layer 170 may be amorphous silicon,silicon-germanium, silicon oxide, silicon nitride, silicon oxynitride,amorphous carbon, or combinations thereof. The mandrel layer materialmay be selectively etchable versus the fin template material and/ormasking layer material.

In one or more embodiments, the photo mask blocks 191 may be removed toexpose the top surface(s) of the one or more mandrel template(s) 181.The photo mask blocks 191 may be removed by known methods (e.g., ashing,stripping, etc.).

FIG. 9 is a cross-sectional side view of a plurality of spacers on thesacrificial mandrels and fin template layer, in accordance with anexemplary embodiment.

In one or more embodiments, spacers 201 may be formed on the sides ofthe sacrificial mandrel(s) 171. The spacers may be formed by deposition(e.g., CVD, ALD or thermal growth (e.g., thermal SiO₂) on the sides ofthe sacrificial mandrels 171. Spacer material may be removed from thesurface of fin template layer 160 by etching back the spacer layermaterial, for example, by RIE.

In various embodiments the spacers 201 may be, for example, siliconoxide (SiO), silicon nitride (SiN), silicon boron carbonitride (SiBCN),silicon oxycarbide (SiOC), etc., where the spacer material may beselectively etchable versus the sacrificial mandrel material and/or fintemplate layer material. In a non-limiting exemplary embodiment, thespacers 201 may be thermally grown silicon oxide (SiO) on the sides ofamorphous silicon sacrificial mandrels 171, where the growth of the SiOmay consume a portion of the sidewalls of the sacrificial mandrels 171.

FIG. 10 is a cross-sectional side view of a plurality of spacers on thefin template layer on the substrate, in accordance with an exemplaryembodiment.

In various embodiments, the mandrel template(s) 181 may be removed toexpose the underlying sacrificial mandrels 171, where the mandreltemplate(s) 181 may be removed by a selective etch, for example aselective RIE.

In one or more embodiments, the sacrificial mandrels 171 may be removedfrom between the spacers 201, where the sacrificial mandrels 171 may beremoved by selective etching, for example a selective RIE. Removal ofthe sacrificial mandrels 171 may expose the underlying fin templatelayer 160 between the spacers 201.

FIG. 11 is a cross-sectional side view of a plurality of spacers on thefin templates and vertical fins, in accordance with an exemplaryembodiment.

In one or more embodiments, portions of the fin template layer 160 notcovered by a spacer 201 may be removed to form fin templates 161. Thespacer pattern may be transferred to the fin template layer 160 forsubsequent formation of a plurality of dummy fins 151 and/or verticalfins 111. In various embodiments, a sidewall image transfer (SIT)technique may be used to form one or more vertical fins 111 and dummyfins 151 on the substrate 110.

In one or more embodiments, portions of the substrate 110 between thefin template(s) 161 may be removed to form one or more vertical fin(s)111. The portions of the substrate 110 may be removed by an anisotropicdry etch, for example, a dry plasma etch. The dry plasma etch may be areactive ion etch (RIE) to provide a directional etch with control ofsidewall etching. One or more dummy fin(s) 151 may be formed by removinga portion of the dummy fin fill 150, where the dummy fin fill may beadjacent to the portion of the substrate 110 also being removed. Thedummy fin fill 150 and substrate 110 may be patterned and etched at thesame time, where the dummy fin fill 150 and substrate 110 may have aboutthe same etch rate for the RIE. A portion of dummy fin fill 150 mayremain in the dummy fin trenches 140 below the dummy fin(s) 151.

In various embodiments, the vertical fin(s) 111 may be formed from thesubstrate material. The substrate 110 may be a single crystal Sisubstrate and the vertical fins may be single crystal silicon. Invarious embodiments, the vertical fin(s) 111 may be suitably doped toform channels of a vertical or horizontal finFET.

In various embodiments, the vertical fin(s) 111 and dummy fin(s) 151 mayhave a width in the range of about 4 nm to about 20 nm, or may have awidth in the range of about 8 nm to about 15 nm, or in the range ofabout 10 nm to about 12 nm. In various embodiments, the vertical fin(s)111 and dummy fin(s) 151 may have substantially the same height andwidth (e.g., within process tolerances/variations).

FIG. 12 is a cross-sectional side view of a plurality of vertical finsand dummy fins in a fin pattern region after removal of the spacers andfin templates, in accordance with an exemplary embodiment.

In one or more embodiments, the spacers 201 and the fin templates 161may be removed to uncover the underlying vertical fin(s) 111 and dummyfin(s) 151. The spacers 201 and fin templates may be removed byselective etches that preferentially remove the spacer material and/orthe fin template material. Two or more etching steps may be employed toremove the spacers 201 and the fin templates 161.

In one or more embodiments, the exposed dummy fin(s) 151 and verticalfin(s) 111 may make up a fin pattern 20 in a fin pattern region 10 onthe substrate 110. The pitch between a dummy fin 151 and an adjacentvertical fin 111 may have been defined by the width and/or position of asacrificial mandrel 171 and/or spacers 201.

In various embodiments, the one or more dummy fin(s) 151 may be locatedat the perimeter of the fin pattern region 10, such that dummy fins 151are also border fins 50, whereas the vertical fins 111 may be interiorfins 90 located within the perimeter and inside the bounds of the borderfins 50.

In one or more embodiments, a doped region 230 may be formed in thesubstrate 110. The doped region 230 may be formed ex-situ below thevertical fin(s) 111. The dummy fin fill 150 in the dummy fin trenches140 may act as a mask to prevent dopant implantation into substrateregions below a subsequent isolation region. One or more doped regions230 may be formed in the substrate above which each of the one or morevertical fins may be formed. The dopant may be provided to the dopedregion(s) 230 by ion implantation, and source/drains formed by annealingthe doped region(s). In various embodiments, the doped region 230 (i.e.,source/drain region) may be n-doped or p-doped. The doped region 230 mayform a bottom source/drain of a vertical fin field effect transistor(vertical finFET). In various embodiments, a plurality of vertical fins111 may be electrically coupled to the same bottom source/drain to forma multi-fin vertical FET. The vertical fin(s) and bottom source/drain(s)may be suitably doped to form an NFET or a PFET.

The formation of a doped region 230 in a substrate may be optional,where a doped region 230 may be formed for fabricating vertical finFETdevices with top and bottom source/drains, whereas a doped region maynot be formed on the substrate 110 for fabrication of finFET(s) withsource/drains at opposite ends of the vertical fin(s) and a horizontalcurrent flow (i.e., horizontal finFETs).

Various embodiments for the fabrication of horizontal finFETs without adoped region 230 (i.e., bottom source/drain) is illustrated in FIGS.14-18, whereas the fabrication of vertical finFET(s) having a dopedregion 230 is illustrated in FIGS. 19-20.

FIG. 13 is a cross-sectional side view of a plurality of vertical finsin a fin pattern region after removal of the dummy fins and fin fill, inaccordance with an exemplary embodiment.

In one or more embodiments, the dummy fins 151 and dummy fin fill 150may be removed to eliminate the border fins 50 that may have differingfin sizes, geometries, and/or profiles than the vertical fin(s) 111 thatare interior fins 90. In various embodiments, the dummy fins 151 may beselectively etched versus the vertical fins 111. In a non-limitingexemplary embodiment, dummy fins 151 made of amorphous silicon,amorphous silicon-germanium, poly-crystalline silicon, orpoly-crystalline silicon-germanium, may be selectively etched by use ofhydrogen chloride gas (gaseous HCl) versus single crystal siliconvertical fins 111.

In various embodiments, after removal of the dummy fin fill 150, a step115 may be present around at least a portion of the periphery of theinterior fins 90, wherein the step 115 may have a height in the range ofabout 5 nm to about 50 nm, or about 10 nm to about 40 nm, from bottom ofthe dummy fin trench 140 to the substrate surface forming a ledge 117adjacent to a vertical fin 111.

While the formation and removal of dummy fin(s) has been shown forborder fins 50 in FIG. 1 and FIGS. 11-13, it is also contemplated thatthe process may also be applied to one or more interior fin(s) 90, as analternative approach to a fin cut process and formation of shallowtrench isolation regions between adjacent finFET devices.

FIG. 14 is a cross-sectional side view of a bottom spacer layer andisolation region formed on a portion of the substrate, in accordancewith an exemplary embodiment.

In one or more embodiments, a dielectric layer 210 may be formed onvertical fins 111, and at least a portion of the substrate 110 includingdummy fin trenches 140. The dielectric layer 210 may be formed by ablanket deposition over the vertical fin(s) 111, where the blanketdeposition may be a conformal deposition, for example, by ALD, CVD, or acombination thereof, or the deposition may be a directional depositionin which the dielectric layer 210 may be formed preferentially on theexposed surfaces of the substrate 110, for example, by PVD and/or gascluster ion beam (GCIB) deposition.

In various embodiments, the dielectric layer 210 may form bottom spacersbetween vertical fin(s) 111 and an isolation region around the verticalfins 111 as part of the same deposition process. The dielectric layer210 may be etched back from the vertical fin(s) 111 to form bottomspacers.

In one or more embodiments, the dielectric layer 210 may be an oxide,for example, silicon oxide (SiO) or a high-k metal oxide, or aninsulating nitride, including but not limited to silicon nitride (SiN),or a silicon oxynitride (SiON).

In various embodiments, the dielectric layer 210 may be a high-Kdielectric material that may include, but is not limited to, transitionmetal oxides such as hafnium oxide (e.g., HfO₂), hafnium silicon oxide(e.g., HfSiO₄), hafnium silicon oxynitride (Hf_(w)Si_(x)O_(y)N_(z)),lanthanum oxide (e.g., La₂O₃), lanthanum aluminum oxide (e.g., LaAlO₃),zirconium oxide (e.g., ZrO₂), zirconium silicon oxide(e.g., ZrSiO₄),zirconium silicon oxynitride (Zr_(w)Si_(x)O_(y)N_(z)), tantalum oxide(e.g., TaO₂, Ta₂O₅), titanium oxide (e.g., TiO₂), barium strontiumtitanium oxide (e.g., BaTiO₃—SrTiO₃), barium titanium oxide(e.g.,BaTiO₃), strontium titanium oxide(e.g., SrTiO₃), yttrium oxide (e.g.,Y₂O₃), aluminum oxide (e.g., Al₂O₃), lead scandium tantalum oxide(Pb(Sc_(x)Ta_(1-x))O₃), and lead zinc niobate (e.g., PbZn_(1/3) Nb_(2/3)O₃). The high-k material may further include dopants such as lanthanumand/or aluminum. The stoichiometry of the high-K compounds may vary.

In one or more embodiments, the portion of the dielectric layer 210between the vertical fins forming a bottom layer may have a thickness inthe range of about 3 nm to about 25 nm, or in the range of about 5 nm toabout 20 nm. The thickness of the bottom spacer layer 140 may provideelectrical isolation of a subsequently formed work function layer(s)and/or a conducting gate electrode layer from a doped source/drainregion 230 in the substrate 110. The portion of the dielectric layer 210in the dummy fin trenches 140 may have a thickness greater than theportion of the dielectric layer 210 between the vertical fins.

FIG. 15 is a cross-sectional side view of a gate dielectric layer formedon the exposed portions of the vertical fins, in accordance with anexemplary embodiment.

In one or more embodiments, a gate dielectric layer 220 may be formed onat least a portion of the vertical fin(s) 111. The gate dielectric layer220 formed on at least opposite sidewalls of the same vertical fin 111may form part of a gate structure of a vertical finFET, where the gatedielectric layer 220 may wrap around the sidewalls and endwalls toencase the vertical fin 111 in the gate dielectric layer 220.

In one or more embodiments, a gate structure may be formed on thevertical fins 111 by depositing a gate dielectric layer 220 on at leasta portion of the exposed sidewall of the vertical fin(s) 111, where thegate dielectric layer 150 may also be formed on at least a portion ofthe dielectric layer 210. The gate dielectric layer 220 may beconformally deposited, for example, by CVD, ALD, or a combinationthereof. Undesired portions of the gate dielectric layer 220 may beremoved by a directional etch, for example, RIE.

In various embodiments, the gate dielectric layer 220 may be a high-Kdielectric material that may include, but is not limited to, metaloxides such as hafnium oxide (e.g., HfO₂), hafnium silicon oxide (e.g.,HfSiO₄), hafnium silicon oxynitride (Hf_(w)Si_(x)O_(y)N_(z)), lanthanumoxide (e.g., La₂O₃), lanthanum aluminum oxide (e.g., LaAlO₃), zirconiumoxide (e.g., ZrO₂), zirconium silicon oxide(e.g., ZrSiO₄), zirconiumsilicon oxynitride (Zr_(w)Si_(x)O_(y)N_(z)), tantalum oxide (e.g., TaO₂,Ta₂O₅), titanium oxide (e.g., TiO₂), barium strontium titanium oxide(e.g., BaTiO₃—SrTiO₃), barium titanium oxide(e.g., BaTiO₃), strontiumtitanium oxide(e.g., SrTiO₃), yttrium oxide (e.g., Y₂O₃), aluminum oxide(e.g., Al₂O₃), lead scandium tantalum oxide (Pb(Sc_(x)Ta_(1-x))O₃), andlead zinc niobate (e.g., PbZn_(1/3) Nb_(2/3) O₃). The high-k materialmay further include dopants such as lanthanum and/or aluminum. Thestoichiometry of the high-k compounds may vary.

FIG. 16 is a cross-sectional side view of a work function layer and agate electrode formed on the gate dielectric layer, in accordance withan exemplary embodiment.

In one or more embodiments, a work function layer 225 may be formed onthe gate dielectric layer 220, where the work function layer may bedeposited over the gate dielectric layer 220 by CVD and/or ALD. The workfunction layer 225 may form part of the gate structure, where the gatestructure may be on one or more vertical fin(s) 111. In variousembodiments, a work function layer 225 may be formed on the gatedielectric layer 220 between the gate dielectric layer 220 and the gateelectrode layer 240.

In various embodiments, a work function layer 225 may be a conductivenitride, including but not limited to titanium nitride (TiN), titaniumaluminum nitride (TiAlN), hafnium nitride (HfN), hafnium silicon nitride(HfSiN), tantalum nitride (TaN), tantalum silicon nitride (TaSiN),tungsten nitride (WN), molybdenum nitride (MoN), niobium nitride (NbN);a conductive carbide, including but not limited to titanium carbide(TiC), titanium aluminum carbide (TiAlC), tantalum carbide (TaC),hafnium carbide (HfC); and combinations thereof.

In various embodiments, the work function layer 225 may have a thicknessin the range of about 3 nm to about 11 nm, or may have a thickness inthe range of about 5 nm to about 8 nm.

In one or more embodiments, a gate electrode layer 240 may be formed onthe gate dielectric layer 220 and/or work function layer 225, where thegate electrode layer 240 may be a conductive material that forms part ofa gate structure on one or more vertical fin(s) 111. In variousembodiments, the gate electrode layer 240 may be formed on thedielectric layer 210, gate dielectric layer 220, and/or work functionlayer 225. The gate electrode layer 240 may be formed by a blanketdeposition that covers a portion of one or more vertical fins 111, forexample, by ALD, CVD, PVD, or a combination thereof. A masking layer maybe formed before depositing the gate electrode layer 240 to define theregions to be covered by the gate electrode layer, as would be known inthe art. The gate electrode layer may extend above the masking layer,and may be at least partially removed by CMP. The masking layer may beremoved after formation of the gate electrode layer, as would be knownin the art.

In various embodiments, portions of the gate dielectric layer 220 andwork function layer 225 may be removed from portions of the verticalfin(s) 111 where source/drains may subsequently be formed.

In various embodiments, the gate structure, including a gate dielectriclayer 220, a work function layer 225, and a gate electrode layer 240,may be formed across a plurality of vertical fins 111, where thevertical fins are coupled to the same doped region 230 in the substrate110 forming a bottom source/drain. The plurality of coupled and gatedfins may form a multi-fin horizontal transistor device, which mayinclude source/drains at opposite ends of the vertical fin(s) 111, wherethe vertical fin(s) form the channel(s) of the horizontal transistordevice.

In various embodiments, the gate electrode layer 240 may be a conductivemetal, where the metal may be tungsten (W), titanium (Ti), molybdenum(Mo), cobalt (Co), or a conductive carbon material (e.g., carbonnanotube, graphene, etc.), or any suitable combinations thereof.

In one or more embodiments, a punch-through stop (PTS) 118 may be formedin a lower portion of the one or more vertical fin(s) 111 by implantinga counter-dopant of opposite polarity of the source/drains for the NFETor PFET with a horizontal current flow. The PTS 118 may be formed in atleast a portion of a vertical fin 111 below the intended region of theFET channel. The doping polarity in PTS region is opposite to the dopingpolarity of source/drain so that source and drain are electricallyisolated by two pn junctions between the PTS-to-source and/orPTS-to-drain interface. For example, for an n-type lateral FinFET, thesource/drains are doped with n-type dopants, so a PTS would be dopedwith p-type dopants. The PTS doping may be done by doping techniquesknown in the art, such as implantation.

FIG. 17 is a top view of a gate structure on a plurality of verticalfins with source/drains at opposite ends of the fins, in accordance withan exemplary embodiment.

In one or more embodiments, a portion of the one or more vertical fin(s)forming a device may be implanted with dopant(s) to form source/drain(s)250 at opposite ends of the vertical fin(s). The source/drain may beformed by implantation or other suitable doping techniques known in theart, for example, in-situ doped epitaxy.

In one or more embodiments, the gate structure 260 may be located onapproximately a central portion of the vertical fin(s) 111 between thesource/drains 250. A gate structure formed on a vertical fin for afinFET with current flow parallel to the plane of the substrate (i.e.,laterally) may have a gate length in the range of about 10 nm to about50 nm, or about 20 nm to about 30 nm, although other gate lengths arecontemplated.

FIG. 18 is a top view of a gate structure on a plurality of verticalfins with source/drains at opposite ends of the fins, in accordance withan exemplary embodiment.

In one or more embodiments, source/drains 250 implanted with dopant(s)may be formed at opposite ends of the vertical fin(s), where thesource/drains may be formed across the vertical fins 111 forming amulti-fin device, such that the fins are electrically coupled to thesame source/drains 250 sharing the same gate structure 260. The gatestructure 260 may be located on approximately a central portion of thevertical fin(s) 111 between the source/drains 250. In variousembodiments, the source/drains 250 may be epitaxially grown blocks dopedin-situ during formation.

In one or more embodiments, a dielectric fill 210 may be formed in theone or more fin trench(es) 180 to electrically isolate neighboringvertical fin segments 116. The dielectric fill 210 may be a siliconoxide (SiO), a low-k oxide (e.g., fluorine doped SiO, carbon doped SiO,porous SiO, etc.), or combinations thereof. The dielectric fill 210 maybe an insulating material that forms a shallow trench isolation region.

In various embodiments, the top source/drain 250, bottom source/drain,and vertical fin segments 116 form at least a portion of a verticalfinFET. In various embodiments, the top source/drain 250 and bottomsource/drain may be n-doped or p-doped. The top source/drain 250 andbottom source/drain also may be interchanged.

FIG. 19 is a cross-sectional side view of a top spacer formed on areduced height gate dielectric layer, work function layer, and gateelectrode layer, in accordance with an exemplary embodiment.

In one or more embodiments, portions of the gate electrode layer 240,work function layer 225, and gate dielectric layer 220 may be removed toreduce the height of the gate electrode layer 240, work function layer225, and gate dielectric layer 220 sufficiently below the top surface ofthe vertical fin(s) 111 to allow space for formation of a top spacer 270and a top source/drain to form a vertical finFET.

In various embodiments, the top spacer 270 may be an insulationmaterial, where the top spacer material may be an oxide, for example,silicon oxide (SiO) or a high-k metal oxide, or an insulating nitride,including but not limited to silicon nitride (SiN), or a siliconoxynitride (SiON).

FIG. 20 is a cross-sectional side view of an interlayer dielectric andtop source/drains formed on the top spacer and top portions of thevertical fins, in accordance with an exemplary embodiment.

In one or more embodiments, top source/drains 255 may be formed on thetop portions of one or more vertical fin(s) 111, where the topsource/drains may be epitaxially grown on single crystal verticalfin(s). A doped region 230 in the substrate below the one or morevertical fin(s) 111 may form a bottom source/drain, where thesource/drains may be n-doped or p-doped to form an NFET or a PFET. Invarious embodiments, the source and drain may be on opposite ends of afin, such that a source may be at the top or the bottom, and the drainmay be at the opposite side of the fin from the source, and the verticalfin forms a channel.

In one or more embodiments, an interlayer dielectric 280 may be formedon the top spacer 270 and top source/drains 255, where the interlayerdielectric (ILD) may electrically isolate portions of the verticalfinFET from each other. In various embodiments, electrical contacts maybe formed to the top source/drains 255 and gate structures through theILD 280, where the top source/drains 255 and gate structures may beelectrically coupled together to form multi-fin finFETs.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It should be understood that use of descriptions such as top, bottom,left, right, vertical, horizontal, or the like, are intended to be inreference to the orientation(s) illustrated in the figures, and areintended to be descriptive and to distinguish aspects of depictedfeatures without being limiting. Spatially relative terms, such as“beneath,” “below,” “lower,” “above,” “upper,” and the like, may be usedherein for ease of description to describe one element's or feature'srelationship to another element(s) or feature(s) as illustrated in theFIGs. It will be understood that the spatially relative terms areintended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the FIGs. Forexample, if the device in the FIGs. is turned over, elements describedas “below” or “beneath” other elements or features would then beoriented “above” the other elements or features. Thus, the term “below”can encompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations), andthe spatially relative descriptors used herein may be interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Reference to first, second, third, etc.,feature is intended to distinguish features without necessarily implyinga particular order unless otherwise so stated or indicated. Thus, afirst element discussed herein could be termed a second element withoutdeparting from the scope of the present concept.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

1. A method of forming a fin field effect transistor (finFET) havingfin(s) with reduced dimensional variations, comprising: forming twodummy fin trenches in a substrate, wherein each of the two dummy fintrenches is on opposite sides of a portion of the substrate; forming adummy fin fill in each of the two dummy fin trenches; forming a firstdummy fin from one of the dummy fin fills, a second dummy fin from theother of the two dummy fin fills, and a vertical fin from the portion ofthe substrate between the two dummy fin trenches, wherein the firstdummy fin and second dummy fin are border fins and the vertical fin isan interior fin; and removing the border fins.
 2. The method of claim 1,wherein the border fins and interior fin have a width in the range ofabout 4 nm to about 20 nm.
 3. The method of claim 1, wherein the dummyfin fill and the border fins are made of amorphous silicon (a-Si),poly-crystalline silicon (p-Si), amorphous silicon-germanium (a-SiGe),or poly-crystalline silicon-germanium (p-SiGe).
 4. The method of claim3, wherein the vertical fin is single crystal silicon, and the borderfins are removed by a selective HCl etch.
 5. The method of claim 1,wherein the width of each of the two dummy fin trenches is in the rangeof about 30 nm to about 30 nm.
 6. The method of claim 5, wherein thedepth of each of the two dummy fin trenches is in the range of 2 nm toabout 200 nm.
 7. The method of claim 6, further comprising forming adoped region in the portion of the substrate.
 8. The method of claim 7,further comprising forming a gate structure on the vertical fin.
 9. Themethod of claim 8, forming a punch -through stop in a lower portion ofthe vertical fin.
 10. The method of claim 9, further comprising forminga top source/drain on the vertical fin. 11-20. (canceled)